Add bradjones1 as Serialization subsystem maintainer

There is no active maintainer for Serialization. This creates a significant roadblock to receiving code review and commit-readiness checks for Serialization components. As this is a lower-level API with no UI, and isn't currently a sexy/flashy initiative, this subsystem goes a bit unnoticed. I would like to have some additional "official" involvement to help advocate for this subsystem and move along some important but stalled initiatives.

My Drupal.org profile provides a CV of my open-source contribution and track record of contribution to core and contrib.

I also propose removing damiankloip from this subsystem as he is no longer active.